Particularly with the advent of positive legislation in this area, it is something of an understatement to say that a great deal of attention is being paid to the reduction of engine pollutants. Because of the broad applicability of certain aspects of the invention, the disadvantages of present engines will be generally considered particularly regarding this area of emission of pollutants.
Internal combustion devices, such as engines and jet turbines, suffer from substantially incomplete combustion and the generation of large quantities of unacceptable pollutants. These defects are, of course, related and together constitute a serious departure from optimum operating conditions. Although external combustion devices and in particular those employing gaseous fuels, are inherently cleaner burning, such devices are capable of improvement in this area and in addition suffer other disadvantages.
Considering some of the conventional engine types, in Diesel-type engines the direct injection of liquid fuel requires that about two-thirds of the time in each cycle between the instant at which injection starts and chemical combustion is completed be taken up with purely mechanical and thermal procedures involving spray penetration and atomization of the liquid fuel and the vaporization and heating of the atomized fuel to self-ignition temperatures. This can permit the injection of a considerable amount of fuel into the cylinder before ignition occurs, thus causing pseudo-explosive pressure peaks. Such operation not only prevents limiting the cylinder pressure during the cycle to reasonable values but also raises the peak operating temperatures. In addition, the ignition time delay imposes a limit on the engine operating speeds. Further, Diesel type engines use a very high compression pressure to ensure that the final compression temperature, starting from low ambient temperatures, is sufficient to supply heat to the atomized fuel and still remain at or above self-ignition temperatures. These high pressures require stronger and hence heavier weight components and combined with the speed limitations of the combustion cycle, represent serious disadvantages. These remarks, of course, also apply to hot bulb-type Diesel engines, which use an ante-chamber for initial combustion and inject the contents of the ante-chamber into the main cylinder space, particularly regarding speed and maximum power restrictions.
Both Diesel type and spark ignition engines permit, and, in general, strive for, the development of high peak temperatures during the cycle. As discussed in more detail hereinbelow, the formation of oxides of nitrogen is considered to be directly related to such peak temperatures and the attempted elimination or reduction of these serious pollutants has made necessary the addition of expensive and bulky reactor devices or the like to the exhaust line. In this regard, because both Diesel type and spark ignition engines have tended to operate at fuel to air ratios which do not provide sufficient air, considering turbulence factors, to secure complete combustion, current trends have been to inject more air into the exhaust manifold to oxidize the unburned fuel at high temperatures, the usual exhaust manifold being modified to permit this. Such an approach has obvious disadvantages. In a further somewhat related approach exhaust gases are recirculated into the inlet manifold to partially combat the formation of oxides of nitrogen. Among the disadvantages of this approach is that it reduces the power output of the engine and causes problems in vehicle operation.
Carburetor type engines also suffer other disadvantages such as problems regarding providing equal cylinder distribution of the combustible flow as well as regarding vaporization under varying conditions. Carburetor icing caused by a temperature drop in the venturi flow is also a problem. Further, carburetor type engines have cold starting difficulties which require such over-rich fuel mixtures so as to be incompatable with acceptable pollutant emissions. In this regard, it is noted that the engine starting period causes higher than average pollutant emissions for all conventional engines.
Other engine types suffer other disadvantages. For example, turbine engines, using liquid fuels injected into compressed air from the compressor, suffer from incomplete combustion and the high temperature formation of oxides of nitrogen. On the other hand, engines burning propane gas are encumbered with bulky fuel supply tanks and are limited insofar as available recharging facilities are concerned.
The literature, of course, includes extensive discussions of the various approaches taken in the area of pollutant emissions control. It should be noted that, apart from approaches involving improved ignition timing, devices employing these approaches largely act downstream of the engine to provide such control. However, it is thought that, rather than discuss these approaches in more detail or, more generally, rather than discuss the various engines referred to hereinabove in more detail than has been done, a greater understanding of the disadvantages of the prior art engines and pollutant control techniques and the advantages of the present invention can be gained through considering the present invention itself.